High power switch mode power supply (SMPS) battery chargers require synchronous rectification converters to achieve high efficiency. However, when the synchronous rectification converter operates in a discontinuous conduction mode (DCM) there is a possibility that the synchronous rectification converter will draw current from the battery being charged for a short period of time and inject that current into the input side (power source) of the synchronous rectification converter. In addition, efficiency of the SMPS suffers because the rectification transistor may discharge the output capacitor during DCM operation. This phenomenon is called battery current reversal and may lead to destruction of the synchronous rectification converter of the SMPS. Battery current reversal in an SMPS never happens when using diode rectification in an asynchronous rectification converter because the diode only lets current flow in one direction (correct direction) compared to a power metal oxide semiconductor field effect transistor (MOSFET) which allows current to flow in both directions. But efficiency is poorer when using an asynchronous rectification converter instead of the more efficient synchronous rectification converter in a SMPS battery charger. This is very important when designing high power capacity battery chargers, e.g., electric vehicle charging stations.
Prior technology solutions to the aforementioned problem of battery current reversal have been putting a power diode in series with the battery under charge but this is not an ideal solution since the power diode will dissipate a great deal of power at high current battery charging levels. Another prior technology solution has been placing a high current switch in series with the battery being charged, but requires additional components of which the high power components can be expensive. Still another prior technology solution has been to force a normally synchronous rectification converter into a diode emulation mode of operation so as to simulate asynchronous operation thereof. This requires a very fast comparator to detect when the SMPS inductor current drops to substantially zero and then contemporaneously thereafter disable the low side power MOSFET until there is inductor current present again.